The present invention relates to a method for determining the pore size distribution of a membrane filter by way of establishing and analyzing the molecular mass distribution curve of the solute fraction in a feed solution that was rejected by the membrane filtration, and an apparatus therefore.
Many kinds of membrane filters, e.g., microfiltration, ultrafiltration and nanofiltration membranes, are used in various water treatment, chemical and food-related processes, and in each application, an accurate membrane pore size measurement is required in order to select a suitable membrane.
Hitherto, the membrane pore size and distribution have been usually measured using electron microscope photography, atomic force microscopy, a liquid displacement method and the like.
Both the electron microscope photography and the liquid displacement method have the disadvantage that they are difficult to apply to ultrafiltration and nanofiltration membranes having small pores. Further, like the electron microscope photography, the atomic force microscopy which measures the membrane pore size using a tip of about 10 nm in diameter has the problem that it is not possible to continuously measure the pore size distribution. Also, these conventional methods all require expensive equipments and cannot be used in determining the pore size of a membrane under the condition of its practical use.
Accordingly, it is an object of the present invention to provide a simple method for continuously monitoring the pore size distribution of a membrane of any type.
It is another object of the present invention to provide an apparatus which is suitable for practicing the method.
In accordance with one aspect of the present invention, there is provided a method for determining the pore size distribution of a membrane, which comprises passing an aquous solution containing nonionic or charged solutes (feed) through the membrane to obtain a filtrate, measuring relative molecular mass distributions of solutes in the feed and the filtrate which are used to assess the molecular mass distribution curve of the solute fraction rejected by the filtration, and calculating the pore size distribution of the membrane based on said distribution curve.
In accordance with another aspect of the present invention, there is provided an apparatus for determining the pore size distribution of a membrane, which comprises a membrane filtration unit with a membrane holder, means for conducting HPLC (High Performance Liquid Chromatography) and SEC (Size Exclusion Chromatography) to measure molecular mass distributions of solutes in the feed and the filtrate, and a software which analyzes the molecular mass distribution results to obtain the pore size distribution of the membrane.